Backrest for a garden bench



FIG. 1 is a front elevational view of a backrest for a garden bench showing my design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a top plan view thereof, the opposite side being a mirror image; and,

FIG. 4 is a right side view thereof, the opposite side being a mirror image. 

The ornamental design for a backrest for a garden bench, as shown and described. 